The invention relates to an indicator having a plurality of belts, intended in particular for connection to the output of a radio altimeter. The indicator has associated with each of the belts, a motor-driven drum. The indicator also has first input for receiving information which is indicated by a first belt denoted "graduated belt", which cooperates with a display window having an index and a graduation. The indicator further includes a second input for receiving reference information for presetting a reference point with respect to the graduated belt. The reference point is marked on a second band denoted the "reference belt".
When such an indicator cooperates with a radio altimeter on board an aircraft, the altitude of the aircraft is given by the first belt and is indicated by a fixed index. There is also a characteristic altitude, denoted the decision altitude, which must be clearly indicated. This altitude is important during landing. When the aircraft is below this decision attitude it must land, even if this would be dangerous in itself, because below this decision altitude it is not possible to restart the engines and to postpone the landing. Because this parameter is of the utmost importance, it is necessary that it is properly visible to the pilot. To this end the decision altitude is indicated by a mark printed on the reference belt. Once this mark has been adjusted to the desired position it must always coincide with that point on the first belt which characterizes the decision altitude, when the point is visible to the user.
In the prior art indicators this is accomplished by means of expensive mechanisms, which are difficult to produce, such as differentials, mechanical coupling and decoupling systems.
It is an object of the invention to provide an indicator which does not require the above-mentioned mechanisms.